This application relates to nucleic acid polymers encoding chimeric T cell receptors (TCRs), to the chimeric TCRs, and to methods of using same to facilitate a T cell response to a selected target.
The induction of potent tumor immunity presents a major challenge for cancer immunotherapy. Tumor cells have many properties that facilitate immune evasion 1-3. Most tumor antigens characterized to date are self-antigens and are thus poorly immunogenic 4,5. The paucity of target antigens, the difficulty of overcoming tolerance to self-antigens, and impaired antigen presentation also contribute to compromise T-cell priming in cancer-bearing hosts 1-3,6-10. Furthermore, malignant cells may escape from tumor-specific effector T cells by downregulating major histocompatibility complex (MHC) and/or antigen expression, or by establishing an immunosuppressive microenvironment 1-3,11.
Genetic approaches offer a potential means to enhance immune recognition and elimination of cancer cells. One promising strategy is to genetically engineer T lymphocytes to express artificial TCRs that direct cytotoxicity toward tumor cells 12,13. Artificial receptors typically comprise a tumor antigen-specific recognition element derived from a single-chain antibody variable fragment (scFv). When used to reprogram T-cell specificity, such fusion receptors permit MHC-independent recognition of native rather than processed antigen 12-14. ScFv-based TCRs are engineered to contain a signaling domain that delivers an activation stimulus (signal 1) only 12-14. The TCR-ζ cytoplasmic domain, which delivers a potent signal 1 in the absence of the remaining components of the TCR-CD3 complex 15,16, is well suited for activating cytolytic functions. The potential clinical utility of this strategy is supported by the demonstration that, despite fears about defective signaling in lymphocytes of tumor-bearing subjects 17, ζ-chain fusion receptors retain potent activity in cancer patent cytotoxic T cells 18.
However, while sufficient to elicit tumoricidal functions, the engagement of ζ-chain fusion receptors may not suffice to elicit substantial IL-2 secretion in the absence of a concomitant co-stimulatory signal 18. In physiological T-cell responses, optimal lymphocyte activation requires the engagement of one or more co-stimulatory receptors (signal 2), the best characterized of which is CD28 19-22. Provision of signal 1 in the absence of CD28 signaling can result in a very poor T-cell proliferative response or in the induction of anergy or apoptosis 19-22. Consequently, it may be extremely valuable to engineer human T cells so that they receive a co-stimulatory signal in a tumor antigen-dependent manner. An important development in this regard has been the successful design of scFv-CD28 fusion receptors that transduce a functional antigen-dependent co-stimulatory signal in human primary T cells, permitting sustained T-cell proliferation when both the endogenous TCR and the chimeric CD28 receptor are engaged 23. See U.S. patent application Ser. No. 08/940,544.
Notwithstanding the foregoing efforts, there remains a continuing need for more effective chimeric TCRs. The present invention offers chimeric TCRs that are able to provide both the activation and the co-stimulation signals from a single molecule to more effectively direct T-lymphocyte cytotoxicity against a defined target and T-lymphocyte proliferation. ζ